Solventless, polyester dipping varnishes, useful for impregnating mica tape already wrapped around electrical coils are well known, and taught by Sattler, in U.S. Pat. No. 4,077,925. The Sattler dipping varnish has a 155.degree. C. to 175.degree. C. insulating capability, a 145.degree. C. to 150.degree. C. flash point, and outstanding pot life properties. That varnish contained an alkyl component having a low equivalent percent of fatty acid and a high equivalent percent of polyhydric alcohol.
While useful as a dipping varnish, the Sattler resin was not completely suitable for impregnating glass fiber wrapping tapes used as a cured, flexible, final bonding for electrical coils; where the impregnating resin requires complete compatibility with glass cloth, very low viscosity, a substantial amount of flexibility, even after baking to cure, and preferably a 180.degree. C. insulating capability. What is needed is a solventless insulating varnish, ,that will easily wet glass cloth, and provide impregnated glass fiber bonding tapes that are still flexible even after a bake to cure cycle.